Highly Efficient Synthesis of Monodisperse Poly(ethylene glycols) and Derivatives through Macrocyclization of Oligo(ethylene glycols)

Jellyfish-inspired smart tetraphenylethene lipids with unique AIE fluorescence, thermal response, and cell membrane interaction

Smart lipids with fluorescence emission, thermal response, and polyethylene glycolation (PEGylation) functions can be highly valuable for formulation, image-traceable delivery, and targeted release of payloads. Herein, a series of jellyfish-shaped amphiphiles with a tetraphenylethene (TPE) core and four symmetrical amphiphilic side chains were conveniently synthesized and systematically investigated as smart lipids. Compared with regular amphiphilic TPE lipids and phospholipids, the unprecedented jellyfish-shaped molecular geometry was found to enable a series of valuable capabilities, including sensitive and responsive aggregation-induced emission of fluorescence (AIE FL) and real-time FL monitoring of drug uptake. Furthermore, the jellyfish-shaped geometry facilitated the concentration-dependent aggregation from unimolecular micelles at low concentrations to "side-by-side" spherical aggregates at high concentrations and a unique mode of AIE. In addition, the size and the arrangement of the amphiphilic side chains were found to dominate the aggregate stability, cell uptake, and thus the cytotoxicity of the amphiphiles. This study has unprecedentedly developed versatile smart TPE lipids with precise structures, and unique physicochemical and biological properties while the peculiar structure-property relationship may shed new light on the design and application of AIE fluorophores and functional lipids in biomedicine and materials science.

Design and synthesis of multivalent drug delivery system with CA IX inhibitors as ligands

A multivalent ligand delivery system holds tremendous potential in the field of tumor-targeted drug delivery. It addresses the challenges posed by the low affinity between small molecule ligand receptors and the rapid metabolism of small molecule drug conjugates (SMDCs) in vivo. Notably, existing multivalent ligand systems have demonstrated significant anti-tumor activity in various tumor models. In this study, we have developed a novel multivalent ligand delivery system for SN38, utilizing acetazolamide, a carbonic anhydrase IX (CA IX) inhibitor, as the target ligand. Our multivalent ligand delivery systems exhibited superior metabolic stability and enhanced targeting specificity compared to SMDC molecules. Furthermore, they demonstrated improved anti-proliferation activity, addressing the existing challenges associated with the low receptor affinity and rapid metabolism of SMDCs.

One-Pot Synthesis of Monofunctionalized Oligoethylene Glycols through Ring-Opening and Heterogeneous Hydrolysis of Macrocyclic Sulfates

The one-pot nucleophilic ring-opening reaction of oligoethylene glycol macrocyclic sulfates provides an efficient strategy for the monofunctionalization of oligoethylene glycols without protecting or activating group manipulation. In this strategy, the hydrolysis process is generally promoted by sulfuric acid, which is hazardous, difficult to handle, environmentally unfriendly, and unfit for industrial operation. Here, we explored a convenient handling solid acid, Amberlyst-15, as a replacement for sulfuric acid to accomplish the hydrolysis of sulfate salt intermediates. With this method, 18 valuable oligoethylene glycol derivatives were prepared with high efficiency, and gram-scale applicability of this method has been successfully demonstrated to afford a clickable oligoethylene glycol derivative 1b and a valuable building block 1g for F-19 magnetic resonance imaging traceable biomaterial construction.

Self-Assembly of Precisely Fluorinated Albumin for Dual Imaging-Guided Synergistic Chemo-Photothermal-Photodynamic Cancer Therapy

Although albumin has been extensively used in nanomedicine, it is still challenging to fluorinate albumin into fluorine-19 magnetic resonance imaging (¹⁹F MRI)-traceable theranostics because existing strategies lead to severe ¹⁹F signal splitting, line broadening, and low ¹⁹F MRI sensitivity. To this end, 34-cysteine-selectively fluorinated bovine serum albumins (BSAs) with a sharp singlet ¹⁹F peak have been developed as ¹⁹F MRI-sensitive and self-assembled frameworks for cancer theranostics. It was found that fluorinated albumin with a non-binding fluorocarbon and a long linker is crucial for avoiding ¹⁹F signal splitting and line broadening. With the fluorinated BSAs, paclitaxel (PTX) and IR-780 were self-assembled into stable, monodisperse, and multifunctional nanoparticles in a framework-promoted self-emulsion way. The high tumor accumulation, efficient cancer cell uptake, and laser-triggered PTX sharp release of the BSA nanoparticles enabled ¹⁹F MRI-near infrared fluorescence imaging (NIR FLI)-guided synergistic chemotherapy (Chemo), photothermal and photodynamic therapy of xenograft MCF-7 cancer with a high therapeutical index in mice. This study developed a rational synthesis of ¹⁹F MRI-sensitive albumin and a framework-promoted self-emulsion of multifunctional BSA nanoparticles, which would promote the development of protein-based high-performance biomaterials for imaging, diagnosis, therapy, and beyond.

Separation of Molar Weight-Distributed Polyethylene Glycols by Reversed-Phase Chromatography—Analysis and Modeling Based on Isocratic Analytical-Scale Investigations

The separation of polyethylene glycols (PEGs) into single homologs by reversed-phase chromatography is investigated experimentally and theoretically. The used core–shell column is shown to achieve the baseline separation of PEG homologs up to molar weights of at least 5000 g/mol. A detailed study is performed elucidating the role of the operating conditions, including the temperature, eluent composition, and degree of polymerization of the polymer. Applying Martin’s rule yields a simple model for retention times that holds for a wide range of conditions. In combination with relations for column efficiency, the role of the operating conditions is discussed, and separations are predicted for analytical-scale chromatography. Finally, the approach is included in an efficient process model based on discrete convolution, which is demonstrated to predict with high accuracy also advanced operating modes with arbitrary injection profiles.

Synthesis of symmetrical secondary oligoethylene glycolated amines from diethanolamine

Monodisperse oligoethylene glycols (M-OEGs)-containing symmetrical secondary amines are highly valuable synthetic intermediates in drug development and materials sciences. Scalable three-step synthesis of M-OEGs secondary amines with flexible M-OEGs and/or alkyl chains is described herein. Through reduction amination of diethanolamine, Williamson ether synthesis, and subsequent deprotection, a series of M-OEGs secondary amines with diverse and fine-tunable chemical structures were conveniently prepared. The presented strategy is attractive with readily available starting materials, simple catalytic systems, scalable synthesis, and avoids the use of explosive sodium azide.

Determination of the critical chain length for macromolecular crystallization using structurally flexible polyketones

Critical chain length that divides small molecular crystallization from macromolecular crystallization is an important index in macro-organic chemistry to predict chain-length dependent properties of oligomers and polymers. However, extensive researches...

Stepwise PEG synthesis featuring deprotection and coupling in one pot

The stepwise synthesis of monodisperse polyethylene glycols (PEGs) and their derivatives usually involves using an acid-labile protecting group such as DMTr and coupling the two PEG moieties together under basic Williamson ether formation conditions. Using this approach, each elongation of PEG is achieved in three steps – deprotection, deprotonation and coupling – in two pots. Here, we report a more convenient approach for PEG synthesis featuring the use of a base-labile protecting group such as the phenethyl group. Using this approach, each elongation of PEG can be achieved in two steps – deprotection and coupling – in only one pot. The deprotonation step, and the isolation and purification of the intermediate product after deprotection using existing approaches are no longer needed when the one-pot approach is used. Because the stepwise PEG synthesis usually requires multiple PEG elongation cycles, the new PEG synthesis method is expected to significantly lower PEG synthesis cost.

Chain-end functionalization of living helical polyisocyanides through a Pd(ii)-mediated Sonogashira coupling reaction

Various functional helical polymers were constructed through chain-end functionalization of living helical polyisocyanides through a Pd(ii)-mediated Sonogashira coupling reaction.

Perfluoro-tert-butanol: a cornerstone for high performance fluorine-19 magnetic resonance imaging

As a versatile quantification and tracking technology, 19F magnetic resonance imaging (19F MRI) provides quantitative "hot-spot" images without ionizing radiation, tissue depth limit, and background interference. However, the lack of suitable imaging agents severely hampers its clinical application. First, because the 19F signals are solely originated from imaging agents, the relatively low sensitivity of MRI technology requires high local 19F concentrations to generate images, which are often beyond the reach of many 19F MRI agents. Second, the peculiar physicochemical properties of many fluorinated compounds usually lead to low 19F signal intensity, tedious formulation, severe organ retention, etc. Therefore, the development of 19F MRI agents with high sensitivity and with suitable physicochemical and biological properties is of great importance. To this end, perfluoro-tert-butanol (PFTB), containing nine equivalent 19F and a modifiable hydroxyl group, has outperformed most perfluorocarbons as a valuable building block for high performance 19F MRI agents. Herein, we summarize the development and application of PFTB-based 19F MRI agents and analyze the strategies to improve their sensitivity and physicochemical and biological properties. In the context of PFC-based 19F MRI agents, we also discuss the challenges and prospects of PFTB-based 19F MRI agents.

Degradable High Molecular Weight Monodisperse Dendritic Poly(ethylene glycols)

Poly(ethylene glycols) (PEGs) are extensively explored by the pharma industry as foundations for new therapeutic products. PEGs are typically used for their conjugation to active drugs, peptides, and proteins and the likeliness to increase the half-life and enhance the therapeutic outcome. Considering the necessity of batch-to-batch consistency for clinical products, monodisperse PEGs are highly attractive but are generally limited to 5 kDa as an upper molecular weight (M_w) and with an oligomer purity of 95%. By amalgamating short, monodisperse PEGs with dendritic frameworks based on 2,2-bis(methylol)propionic acid polyesters, we showcase a robust synthetic approach to monodisperse PEGs with M_w ranging from 2 to 65 kDa. The latter is, to our knowledge, the highest M_w structure of its kind ever reported. Importantly, the dendritic multifunctional connector facilitated degradability at pH 7.4 at 37 °C, which is an important feature for the delivery of therapeutic agents.

Monodisperse and Polydisperse PEGylation of Peptides and Proteins: A Comparative Study

Although PEGylation is widely used in biomedicine with great success, it suffers from many drawbacks, such as polydispersity, nonbiodegradability, and loss of precursor potency. Recently, the search for polyethylene glycol (PEG) substitutes has attracted considerable attention. Some of the substitutes partially address the drawbacks of PEGs, but sacrifice the "stealth" effect of PEGs and bring in new issues. Herein, we developed monodisperse oligoethylene glycol (M-OEG) polyamides over 5000 Da as biodegradable and monodisperse PEGylation (M-PEGylation) agents, which provided M-PEGylated peptides and proteins with high monodispersity and a biodegradable PEG moiety. Compared to regular PEGylated proteins with a complex "stealth" cloud of PEG, the hydrogen bond interactions between the M-OEG polyamides and proteins provided the M-PEGylated protein with a biodegradable "stealth" cloak. The monodisperse and biodegradable M-PEGylation strategy as well as the peculiar protein-M-OEG polyamide interactions may shed light on many long-lasting issues during the development of PEGylated biologic drugs, such as monodispersity, biodegradability, and tunable conformation.

Synthesis of Stable Cholesteryl-Polyethylene Glycol-Peptide Conjugates with Non-Disperse Polyethylene Glycol Lengths

A method for conjugating cholesterol to peptide ligands through non-disperse polyethylene glycol (ND-PEG) through a non-hydrolysable linkage is described. The iterative addition of tetraethylene glycol macrocyclic sulfate to cholesterol (Chol) renders a family of highly pure well-defined Chol-PEG compounds with different PEG lengths from 4 up to 20 ethylene oxide units, stably linked through an ether bond. The conjugation of these Chol-PEG compounds to the cyclic (RGDfK) peptide though Lys5 side chains generates different lengths of Chol-PEG-RGD conjugates that retain the oligomer purity of the precursors, as analysis by HRMS and NMR has shown. Other derivatives were synthesized with similar results, such as Chol-PEG-OCH3 and Chol-PEG conjugated to glutathione and Tf1 peptides through maleimide-thiol chemoselective ligation. This method allows the systematic synthesis of highly pure uniform stable Chol-PEGs, circumventing the use of activation groups on each elongation step and thus reducing the number of synthesis steps.

Peptidic Monodisperse PEG "Comb" as Multifunctional "Add-On" Module for Imaging-Traceable and Thermo-Responsive Theranostics

Monodisperse polyethylene glycols-modified (M-PEGylated) biomaterials exhibit high structural accuracy, biocompatibility, and fine-tunable physicochemical properties. To develop "smart" drug delivery systems in a controllable and convenient manner, a peptidic M-PEG "comb" with fluorinated L-lysine side chains and a fluorescent N-terminal is conveniently prepared as a ¹⁹ F magnetic resonance imaging (¹⁹ F MRI) and fluorescence dual-imaging traceable and thermo-responsive "add-on" module for liposomal theranostics in cancer therapy. The peptidic M-PEG "comb" has high biocompatibility, thermo-responsivity with a sharp lower critical solution temperature, an aggregation-induced emission fluorescence, and high ¹⁹ F MRI sensitivity. As a highly branched amphiphile, it self-assembles and firmly anchors on the doxorubicin-loaded liposomal nanoparticles, which M-PEGylates the liposomes and facilitates the thermo-responsive drug release and drug tracking with dual-imaging technologies. In a rodent xenograft model of human liver cancer HepG2 cells, the M-PEGylated liposomes exhibit long in vivo half time, low toxicity, high tumor accumulation, "hot spot" ¹⁹ F MRI, and therapeutic efficacy. With accurately programmable chemical structure, fine-tunable physicochemical and biological properties to meet the demands of diagnosis, drug delivery, and therapy, the M-PEG "comb" is promising as a versatile "add-on" module for rapid and convenient formulation of various "smart" theranostics.

Monodisperse polyethylene glycol "brushes" with enhanced lipophilicity, and thermo and plasma stability

A convenient strategy was developed for highly branched and multifunctionalized peptidic monodisperse polyethylene glycol "brushes", which exhibit remarkable physicochemical and biological properties and potential as versatile biomaterials.

Synthesis of monodisperse isomeric oligomers based on meta-/para- and linear/star-monomer precursors with Ugi–hydrosilylation orthogonal cycles

Monodisperse oligomers were precisely prepared through orthogonal cycles of Ugi-4CRs and hydrosilylation coupling reactions, and the “monodisperse isomeric oligomers” were explored.

Direct comparison of solution and solid phase synthesis of sequence-defined macromolecules

Sequence-defined macromolecules of high molecular weight are synthesised by the combination of click chemistry with multicomponent reactions. The synthesis is performed on solid phase as well as in solution to directly compare the two approaches.

Monodisperse oligoethylene glycols modified Camptothecin, 10-Hydroxycamptothecin and SN38 prodrugs

Camptothecin, which represents a class of natural products with high anticancer activity, suffers low water solubility which hampers its clinic application. To address this issue, monodisperse polyethylene glycols were employed to modify this class of natural products, including Camptothecin, 10-Hydroxycamptothecin, and SN38. Through selective modification with a series of monodisperse polyethylene glycols, 31 Camptothecin derivatives, including 9 ethers and 22 carbonates, were prepared using a macrocyclic sulfate-based strategy with high efficacy. Monodisperse polyethylene glycols modification provided the Camptothecin derivatives with high purity and fine-tunable water solubility. Through the physicochemical and biological assays, a few novel prodrugs with good solubility, cytotoxicity, and valuable drug release profile were identified as promising anticancer drug candidates.

Sequence-defined multifunctional polyethers via liquid-phase synthesis with molecular sieving

Synthetic chemists have devoted tremendous effort towards the production of precision synthetic polymers with defined sequences and specific functions. However, the creation of a general technology that enables precise control over monomer sequence, with efficient isolation of the target polymers, is highly challenging. Here, we report a robust strategy for the production of sequence-defined synthetic polymers through a combination of liquid-phase synthesis and selective molecular sieving. The polymer is assembled in solution with real-time monitoring to ensure couplings proceed to completion, on a three-armed star-shaped macromolecule to maximize efficiency during the molecular sieving process. This approach is applied to the construction of sequence-defined polyethers, with side-arms at precisely defined locations that can undergo site-selective modification after polymerization. Using this versatile strategy, we have introduced structural and functional diversity into sequence-defined polyethers, unlocking their potential for real-life applications in nanotechnology, healthcare and information storage.

One-pot synthesis of monodisperse dual-functionalized polyethylene glycols through macrocyclic sulfates

Dual-functionalization of monodisperse oligoethylene glycols, especially hetero-functionalization, provides a series of highly valuable intermediates for life and materials sciences. However, the existing methods for the preparation of these compounds suffer excessive protecting and activating group manipulation as well as tedious purification. Here, a one-pot dual-substitution strategy with macrocyclic sulfates of polyethylene glycols as the key intermediates was developed for the convenient and scalable preparation of a series of homo-functionalized and hetero-functionalized oligoethylene glycols in just 1 step. A high synthetic efficacy was achieved by avoiding the protecting and activating group manipulation and the intermediate purification.

Solid Phase Stepwise Synthesis of Polyethylene Glycols

Polyethylene glycol (PEG) and derivatives with eight and twelve ethylene glycol units were synthesized by stepwise addition of tetraethylene glycol monomers on a polystyrene solid support. The monomer contains a tosyl group at one end and a dimethoxytrityl group at the other. The Wang resin, which contains the 4-benzyloxy benzyl alcohol function, was used as the support. The synthetic cycle consists of deprotonation, Williamson ether formation (coupling), and detritylation. Cleavage of PEGs from solid support was achieved with trifluoroacetic acid. The synthesis including monomer synthesis was entirely chromatography-free. PEG products including those with different functionalities at the two termini were obtained in high yields. The products were analyzed with ESI and MALDI-TOF MS and were found close to monodispersity.

Rational Design of Dual Active Sites in a Single Protein Scaffold: A Case Study of Heme Protein in Myoglobin

Rational protein design has been proven to be a powerful tool for creating functional artificial proteins. Although many artificial metalloproteins with a single active site have been successfully created, those with dual active sites in a single protein scaffold are still relatively rare. In this study, we rationally designed dual active sites in a single heme protein scaffold, myoglobin (Mb), by retaining the native heme site and creating a copper-binding site remotely through a single mutation of Arg118 to His or Met. Isothermal titration calorimetry (ITC) and electron paramagnetic resonance (EPR) studies confirmed that a copper-binding site of [3-His] or [2-His-1-Met] motif was successfully created in the single mutant of R118H Mb and R118M Mb, respectively. UV/Vis kinetic spectroscopy and EPR studies further revealed that both the heme site and the designed copper site exhibited nitrite reductase activity. This study presents a new example for rational protein design with multiple active sites in a single protein scaffold, which also lays the groundwork for further investigation of the structure and function relationship of heme/non-heme proteins.

A Versatile and Scalable Strategy to Discrete Oligomers

A versatile strategy is reported for the multigram synthesis of discrete oligomers from commercially available monomer families, e.g., acrylates, styrenics, and siloxanes. Central to this strategy is the identification of reproducible procedures for the separation of oligomer mixtures using automated flash chromatography systems with the effectiveness of this approach demonstrated through the multigram preparation of discrete oligomer libraries (Đ = 1.0). Synthetic availability, coupled with accurate structural control, allows these functional building blocks to be harnessed for both fundamental studies as well as targeted technological applications.

Chromatography-free synthesis of monodisperse oligo(ethylene glycol) mono-p-toluenesulfonates and quantitative analysis of oligomer purity

Oligo(ethylene glycol) monotosylates are prepared on a multigram scale and in high purity with a new chromatography-free process.

Multigram chromatography-free synthesis of octa(ethylene glycol) p-toluenesulfonate

A detailed synthetic procedure for the chromatography-free synthesis of octa(ethylene glycol) p-toluenesulfonate is reported.

Amide bond-containing monodisperse polyethylene glycols beyond 10 000 Da

Monodisperse polyethylene glycols above 4000 Da, including the longest one to date (10 262 Da), can be prepared from oligoethylene glycol-containing ω-amino acids through solid phase synthesis.